Fighting cancer with heat

Ellis Davies reports on a nanomaterial technology that could help treat cancer more effectively.

A major issue with the treatment of cancer through hyperthermia – a type of therapy in which body tissue is exposed to temperatures of up to 45°C – is the damage it can cause to healthy cells through overheating. Researchers from the University of Surrey, UK, and Dalian University of Technology, China, have developed a potential solution using self-regulating nanoparticles. The method, magnetic hyperthermia, uses nanoparticles to heat the affected cells to a pre-determined temperature to avoid damaging healthy cells.

Magnetic hyperthermia has been developed to treat malignant tumours – which invade surrounding tissues and may recur – and is part of a drive to use nanobiotechnology for the accurate targeting and precise delivery of treatments to cancers that circumvent large doses of typically toxic drugs.

Dr Wei Zhang of the Department of Engineering Mechanics at Dalian University of Technology told Materials World. ‘Magnetic media are introduced to the tumour region, by implantation or intervention, and will generate heat upon the application of a local external alternating magnetic field. Since a temperature higher than 45°C may damage normal tissue, we attempt to self-control the therapy temperature by using the magnetic properties of the nanomaterials,’ he said. If the temperature can be controlled in the range of 42–45°C, tumour cells can be weakened or killed without affecting normal tissue.

The team used zinc (Zn), cobalt (Co) and chromium (Cr) ferrite nanoparticles for this study. Ferrite nanoparticles such as iron oxide (Fe3O4 or Fe2O3) were considered good candidates in clinical trials, but the Curie temperature – the temperature at which ferromagnetic materials lose their intrinsic permanent magnetic properties and their ability to generate heat under an alternating magnetic field – of iron oxide nanoparticles is quite high (several hundred degrees) and the hyperthermia temperature cannot be regulated by itself. Therefore, the team added Zn, Co and Cr to decrease the Curie temperature to ensure their function. These nanoparticles are prepared from metal salts (FeCl3, ZnCl2, CoCl2 and CrCl3) using a hydrothermal method.

The nanoparticles were prepared with a Curie temperature as low as 34°C, which means that they can function in the body, unlike other Fe nanoparticles that require much more heat. When the temperature of the nanoparticles falls below 45°C they will generate heat under an applied alternating magnetic field. When the nanoparticles reach the desired therapy temperature (42–45°C), they will lose their magnetic properties and will stop generating heat. ‘Therefore, these nanoparticles could self-regulate the given therapy temperature and avoid damaging healthy tissue by overheating,’ said Zhang. ‘In a respect, the nanoparticles are much like a therapy temperature intrigued switch that can automatically switch on and off, maintaining the therapy temperature.’

They could be injected into tumour regions. Since normal cells possess higher heat resistance and resilience than tumorous, these can be killed without affecting normal tissue.

Cytotoxicity tests have been conducted, and the team is now using the nanoparticles on animals, with the final target being clinic application. The use of such nanoparticles in cancer treatment could do away with clumsy and expensive temperature monitoring and controlling systems, which can also cause inflammatory reactions in the patient's body.

Overall, the development has the potential to prevent damage to healthy tissue, caused by over heating and to reduce the side effects of cancer treatment.

‘This could potentially be a game changer in the way we treat people who have cancer [...] This is a major nanomaterials breakthrough,’ added Zhang.